[GitHub] [bookkeeper] eolivelli commented on a change in pull request #2742: Abstract the FileChannel in the JournalChannel

[GitBox <gi...@apache.org>]

eolivelli commented on a change in pull request #2742:
URL: https://github.com/apache/bookkeeper/pull/2742#discussion_r690937048



##########
File path: bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/FileChannelProvider.java
##########
@@ -0,0 +1,54 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.bookkeeper.bookie;
+
+import java.io.File;
+import java.io.IOException;
+import org.apache.bookkeeper.conf.ServerConfiguration;
+
+/**
+ * An interface of the FileChannelProvider.
+ */
+public interface FileChannelProvider {
+    /**
+     *
+     * @param providerClassName Provided class name for file channel.
+     * @return
+     * @throws IOException
+     */
+    static FileChannelProvider newProvider(String providerClassName) throws IOException {
+        try {
+            Class<?> providerClass = Class.forName(providerClassName);
+            Object obj = providerClass.getDeclaredConstructor().newInstance();

Review comment:
       it is better to use `getConstructor()` instead of `getDeclaredConstructor()` (includes "private" methods)

##########
File path: bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/DefaultFileChannelProvider.java
##########
@@ -0,0 +1,70 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.bookkeeper.bookie;
+
+import java.io.File;
+import java.io.FileDescriptor;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.channels.FileChannel;
+import org.apache.bookkeeper.conf.ServerConfiguration;
+
+/**
+ * A wrapper of FileChannel.
+ */
+public class DefaultFileChannelProvider implements FileChannelProvider{
+    @Override
+    public BookieFileChannel open(File file, ServerConfiguration configuration) throws IOException {
+        return new DefaultFileChannel(file, configuration);
+    }
+
+    static class DefaultFileChannel implements BookieFileChannel {
+        private final File file;
+        private RandomAccessFile randomAccessFile;
+        private final ServerConfiguration configuration;
+
+        DefaultFileChannel(File file, ServerConfiguration serverConfiguration) throws IOException {
+            this.file = file;
+            this.configuration = serverConfiguration;
+        }
+
+        @Override
+        public FileChannel getFileChannel() throws FileNotFoundException {
+            synchronized (this) {
+                if (randomAccessFile == null) {
+                    randomAccessFile = new RandomAccessFile(file, "rw");
+                }
+                return randomAccessFile.getChannel();
+            }
+        }
+
+        @Override
+        public boolean fileExists(File file) {
+            return file.exists();
+        }
+
+        @Override
+        public FileDescriptor getFD() throws IOException {
+            synchronized (this) {
+                return randomAccessFile.getFD();

Review comment:
       NPE?
   I suggest to throw IOException if the handle is null
   Or to initialise it by calling `getFileChannel`




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